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1.
Dalton Trans ; 50(35): 12316-12323, 2021 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-34519737

RESUMO

Oxidative degradation and transformation of catalysts are commonly observed in water oxidation by molecular catalysts, especially when a highly oxidizing reagent such as (NH4)2[Ce(NO3)6] [Ce(IV)] is used. We report herein the synthesis of a ruthenium(III) complex bearing an oxidative resistant bipyridine-bis(alkoxide) ligand, [Ru(bdalk)(pic)2]+ (1, H2bdalk = 2,2'-([2,2'-bipyridine]-6,6'-diyl)bis(propan-2-ol), pic = 4-picoline) as a water oxidation catalyst (WOC). A ruthenium(II) nitrosyl complex [Ru(Hbdalk)(NO)(pic)2]2+ (3) was also formed during the water oxidation process by 1/Ce(IV), and was isolated and structurally characterized. Complex 3 was found to be an active WOC, with the nitrosyl group remaining intact during water oxidation.

2.
ChemSusChem ; 10(20): 4009-4013, 2017 10 23.
Artigo em Inglês | MEDLINE | ID: mdl-28840967

RESUMO

The invention of efficient systems for the photocatalytic reduction of CO2 comprising earth-abundant metal catalysts is a promising approach for the production of solar fuels. One bottleneck is to design highly selective and robust molecular complexes that are able to transform the CO2 gas. The CuII quaterpyridine complex [Cu(qpy)]2+ (1) is found to be a highly efficient and selective catalyst for visible-light driven CO2 reduction in CH3 CN using [Ru(bpy)3 ]2+ (bpy: bipyridine) as photosensitizer and BIH/TEOA (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole/triethanolamine) as sacrificial reductant. The photocatalytic reaction is greatly enhanced by the presence of H2 O (1-4 % v/v), and a turnover number of >12 400 for CO production can be achieved with 97 % selectivity, which is among the highest of molecular 3d CO2 reduction catalysts. Results from Hg poisoning and dynamic light scattering experiments suggest that this photocatalyst is homogenous. To the best of our knowledge, 1 is the first example of molecular Cu-based catalyst for the photoreduction of CO2 .


Assuntos
Dióxido de Carbono/química , Monóxido de Carbono/química , Cobre/química , Compostos Organometálicos/química , Processos Fotoquímicos , Piridinas/química , Catálise , Eletroquímica , Oxirredução
3.
J Am Chem Soc ; 138(30): 9413-6, 2016 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-27443679

RESUMO

The design of highly efficient and selective photocatalytic systems for CO2 reduction that are based on nonexpensive materials is a great challenge for chemists. The photocatalytic reduction of CO2 by [Co(qpy)(OH2)2](2+) (1) (qpy = 2,2':6',2″:6″,2‴-quaterpyridine) and [Fe(qpy)(OH2)2](2+) (2) have been investigated. With Ru(bpy)3(2+) as the photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the sacrificial reductant in CH3CN/triethanolamine solution under visible-light excitation (blue light-emitting diode), a turnover number (TON) for CO as high as 2660 with 98% selectivity can be achieved for the cobalt catalyst. In the case of the iron catalyst, the TON was >3000 with up to 95% selectivity. More significantly, when Ru(bpy)3(2+) was replaced by the organic dye sensitizer purpurin, TONs of 790 and 1365 were achieved in N,N-dimethylformamide for the cobalt and iron catalysts, respectively.

4.
Angew Chem Int Ed Engl ; 55(1): 288-91, 2016 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-26554748

RESUMO

Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [Os(V)(O)(qpy)(pic)Cl](2+) (qpy = 2,2':6',2'':6'',2'''-quaterpyridine, pic = 4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C-H bond dissociation energy as high as 90 kcal mol(-1). This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species.

5.
Chem Commun (Camb) ; 50(95): 14956-9, 2014 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-25327382

RESUMO

A double-helical dicobalt(II) complex [Co2(spy)2](ClO4)4 (spy = 2,2':6',2″:6″,2‴:6‴,2'''':6'''',2'''''-sexipyridine) (1) is found to catalyze visible light-induced water oxidation by [Ru(bpy)3](2+)/Na2S2O8, with a maximum turnover number of 442. Several lines of evidence suggest that functions as a molecular catalyst and does not produce any CoOx in water oxidation.

6.
Angew Chem Int Ed Engl ; 53(52): 14468-71, 2014 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-25348095

RESUMO

Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)2 ](2+) (qpy=2,2':6',2'':6'',2'''-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce(IV) -driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy-N,N'''-dioxide (ONNO) complexes [Ru(ONNO)(L)2 ](3+) which are the real catalysts for water oxidation.


Assuntos
Complexos de Coordenação/química , Piridinas/química , Rutênio/química , Água/química , Catálise , Cristalografia por Raios X , Conformação Molecular , Oxirredução
7.
ChemSusChem ; 7(1): 127-34, 2014 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-24155063

RESUMO

Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7-9 in borate buffer. For chemical oxidation, [Ru(bpy)3](3+) (bpy = 2,2'-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s(-1). Notably, simple Ni salts such as Ni(NO3 )2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3](2+) as the photosensitizer and S2 O8 (2-) as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced ß-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.


Assuntos
Complexos de Coordenação/química , Níquel/química , Água/química , Catálise , Complexos de Coordenação/efeitos da radiação , Luz , Nanopartículas Metálicas/química , Níquel/efeitos da radiação , Compostos Organometálicos/química , Compostos Organometálicos/efeitos da radiação , Oxirredução , Rutênio/química , Rutênio/efeitos da radiação , Sais/química , Compostos de Sódio/química , Compostos de Sódio/efeitos da radiação , Sulfatos/química , Sulfatos/efeitos da radiação
9.
Chemistry ; 18(1): 138-44, 2012 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-22139634

RESUMO

In aqueous acidic solutions trans-[Ru(VI)(L)(O)(2)](2+) (L=1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) is rapidly reduced by excess NO to give trans-[Ru(L)(NO)(OH)](2+). When ≤1 mol equiv NO is used, the intermediate Ru(IV) species, trans-[Ru(IV)(L)(O)(OH(2))](2+), can be detected. The reaction of [Ru(VI)(L)(O)(2)](2+) with NO is first order with respect to [Ru(VI)] and [NO], k(2)=(4.13±0.21)×10(1) M(-1) s(-1) at 298.0 K. ΔH(≠) and ΔS(≠) are (12.0±0.3) kcal mol(-1) and -(11±1) cal mol(-1) K(-1), respectively. In CH(3)CN, ΔH(≠) and ΔS(≠) have the same values as in H(2)O; this suggests that the mechanism is the same in both solvents. In CH(3)CN, the reaction of [Ru(VI)(L)(O)(2)](2+) with NO produces a blue-green species with λ(max) at approximately 650 nm, which is characteristic of N(2)O(3). N(2)O(3) is formed by coupling of NO(2) with excess NO; it is relatively stable in CH(3)CN, but undergoes rapid hydrolysis in H(2)O. A mechanism that involves oxygen atom transfer from [Ru(VI)(L)(O)(2)](2+) to NO to produce NO(2) is proposed. The kinetics of the reaction of [Ru(IV)(L)(O)(OH(2))](2+) with NO has also been investigated. In this case, the data are consistent with initial one-electron O(-) transfer from Ru(IV) to NO to produce the nitrito species [Ru(III)(L)(ONO)(OH(2))](2+) (k(2)>10(6) M(-1) s(-1)), followed by a reaction with another molecule of NO to give [Ru(L)(NO)(OH)](2+) and NO(2)(-) (k(2)=54.7 M(-1) s(-1)).


Assuntos
Óxido Nítrico/química , Compostos Organometálicos/química , Oxigênio/química , Rutênio/química , Espectroscopia de Ressonância de Spin Eletrônica , Cinética , Estrutura Molecular , Oxirredução , Soluções , Solventes , Estereoisomerismo , Termodinâmica
10.
Chem Commun (Camb) ; 47(14): 4159-61, 2011 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-21359340

RESUMO

MnO(4)(-) is activated by BF(3) to undergo intramolecular coupling of two oxo ligands to generate O(2). DFT calculations suggest that there should be a spin intercrossing between the singlet and triplet potential energy surfaces on going from the active intermediate [MnO(2)(OBF(3))(2)](-) to the O···O coupling transition state.


Assuntos
Boratos/química , Compostos de Manganês/química , Óxidos/química , Oxigênio/química , Acetonitrilas/química , Cinética , Oxirredução , Termodinâmica
11.
Inorg Chem ; 47(17): 7447-9, 2008 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-18661968

RESUMO

A new class of readily tunable and highly environmentally sensitive luminescent rhenium(I) tetra(isocyano)bipyridyl complexes has been synthesized and characterized, and their luminescent properties have been investigated. Preliminary studies showed that the metal-to-ligand charge-transfer [dpi(Re) --> pi*(bpy)] absorption and emission are extremely sensitive to the nature of the solvent and the rigidity of the environment.


Assuntos
Cianetos/química , Luminescência , Compostos Organometálicos/química , Piridinas/química , Rênio/química , Elétrons , Compostos Organometálicos/síntese química
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